Various technologies have been applied to measure the location, orientation and surface shapes of objects in space.
In the field of robotics it is known to determine the location of a series of rigid, linked elements in space by measuring the angular degree of rotation existing at the various joints joining such linked elements, cf U.S. Pat. No. 5,576,727 to Rosenberg et al.
In the field of interfaces between humans and mechanisms, gonimeters based upon rotary potentiometers or strain gauges are used to measure the angular relationships between parts of the human body, cf, U.S. Pat. No. 5,163,228 to Edwards et al.
U.S. Pat. No. 4,988,981 (Thomas Zimmerman et al) reveals means for sensing body position using flex sensors, including the use of flex sensors carried by a glove. Such gloves have been widely used and reported on. Reported problems include ambiguity of response due to finger motion occurring in multiple degrees of freedom, and other inaccuracies due to fit of the glove to the hand. Similar methods of providing flex sensing in a glove are reported in U.S. Pat. No. 5,097,252 (Y. L. Harvill et al).
Slidable linkage flex sensors designed to sense two degrees of freedom of finger joint motion have been described in U.S. Pat. No.5,316,017 (Glenn Edwards et al). The slidable linkage permits the sensor to accommodate for the changing distance between attachment points during flexure.
U.S. Pat. No. 5,533,531 (Glenn Edwards et al) addresses separating and identifying motions having multiple degrees of freedom (DOFs) using a multi-DOF contacting sensor: the DOFs are exercised separately in a calibration routine, which provides a mathematical relationship between the outputs of the sensors responding to detected motions which can be used to provide separate DOF signals. A similar method is advanced in U.S. Pat. No. 5,531,257 (Danisch), in which three fiber optic sensors mounted in parallel with their sensing surfaces splayed in separate directions are used for resolving bends in multiple DOFs in a flexing structure. However, neither reference suggests methods of dealing with twist, which would cause ambiguity or be undetectable in the readings of either of the patented sensor methods. Nor does either patent deal with the problem of determining the complete position and orientation of a longitudinally extended structure based only on measurement of flexure.
Rotations in a flexure include bending that is transverse to the longitudinal extent of the substrate; and twisting that occurs about an axis which is coincident with the longitudinal extent of the substrate. Both types of bending quality as "flexures".
Twist is usually negligible in sensor structures based on cylinders, rods, and other solids with significant cross-sectional dimensions. However, it can be very advantageous to measure the presence of twist in flat, ribbon-like flexures. Such flexures are very convenient for incorporation in garments.
Viral Technologies Inc. of Palo Alto Calif. markets an instrumented fabric glove which incorporates bend sensors at the finger joints and other sensors for measuring thumb cross-over, palm arch, wrist flexion and wrist adjunction. The position of the glove and its sensors in space is also measurable by coupling the glove wristband to a 6 degrees-of-freedom space-position tracking mechanism.
An instrumented glove marketed by General Reality Company of San Jose Calif. relies upon fiber optic bend sensors to sense bending at various points on the glove.
In the field of animation motion capture, procedures are used to record the positions and movements of the human body. One method has involved visually capturing the locations in space of "target" markers carried on the limbs and bodies of human actors. Another methods has been to provide an "exoskeleton" mechanical structure which acts as a mechanism in following, and providing signals for recording, the motions and positions assumed by the human body. Accuracy is then limited by the ability of the exoskeleton to maintain a stable mounting to the body. The penalty of such systems is the constricting and cumbersome nature of mechanical exoskeletons. Also, it is very difficult, if not impossible, to build exoskeletons that permit full limb movement or that can account for all limb rotations and other subtle multiple degree of freedom limb movements. Further, exoskeletons are generally removed a significant distance from the measured surface, leading to their inaccuracy and increased bulk.
Both of the target marker and exoskeleton methods as presently conceived are complex and entail inconveniences in their implementation. A need exists for a light weight, unencumbering, position and motion sensing device that can conveniently track and identify the location and geometric configuration of objects in space. The invention herein addresses such an objective.
More particularly an object of the present invention is to provide a flexural reference platform equipped with distributed sensors wherein changes in the shape of the platform are sensed by the sensors in such a way that the complete shape of the platform can be found by calculations from the outputs of the sensors.
Another object of this invention is to provide an instrumented, flexible member that is sufficiently compliant to substantially conform to the surface of a curved object and act as a sensor to provide electronically processable data as to the shape of that surface.
A variety of technologies exist for measuring the state of flexure--bend and twist--in an object. A convenient class of technology particularly suited to this objective relies on fiber optics.
U.S. Pat. No. 5,321,257 to Danisch describes a modified optical fiber that is provided with a light absorbent region on a portion of the outer fiber surface whereby the curvature at such modified region may be remotely detected by the change in the overall light transmission capacity of the fiber. This patent depicts the deployment of clusters of modified fibers capable of detecting a bend in three dimensional shape (FIG. 12).
Patent Co-operation Treaty application PCT/CA94/00314 (published Dec. 22, 1994 as WO 94/29671) discloses the use of looped fiber optic light wave guides to measure curvature. The fiber is looped to provide outgoing and return wave paths that pass through a looped end that effects a 180 degree bend. The surface of the fiber is treated adjacent to and within the curvature of the looped portion to render it absorbent of light. In one configuration it is the side of the fiber surface lying along the top plane of the looped end that is treated. Once the looped end is so treated, it is sensitive to its state of curvature when deflected out of or through the normally flat plane of the loop. Such flexure can be detected remotely by the change of intensity in returning light carried by the fiber. This provides a measure of localized curvature in the region of the loop.
A further paper on this subject by the inventor herein entitled "Laminated Beam Loops" has been published in SPIE Vol. 2839, pp. 311-322, 1996. The contents of this paper, the above referenced U.S. patents and the published PCT application PCT/CA94/00314 are all adopted by reference herein.
Looped optical fiber sensors can measure bend and, in accordance with the invention hereafter described, twist based on the disposition of the loop and the location of the treated, light absorbing region of the fiber surface adjacent to or within the loop. The sensitive region at the looped end of the fiber can be contained within a running length of on the order to three millimeters to a few centimeters depending on desired sensitivity and the diameter of the fibers. This provides a corresponding span for the sampling of the average state of curvature of the sensing looped end of the optic fiber.
Fiber optic technology is convenient for use in sensors because it is robust, benign and inexpensive. A need exists for a fiber-optic based sensor system that can provide remote information on the locations of objects in space, the shape of surfaces and changes in the shape of surfaces. The present invention addresses such a need.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.